Second Black Hole Merger Observed by LIGO

Gravitational waves from second event point to coalescence of smaller black holes

June 15, 2016 | David Voss

Four months after the first announcement that gravitational waves had been directly observed from a merger of two black holes, the LIGO and VIRGO collaborations have now seen a second merger. In a paper in the APS journal Physical Review Letters, they report that the second signal was detected in December 2015 (about 1.4 billion years after the actual event). The paper is accompanied by a Focus article in Physics.

This second merger involved black holes with 8 and 14 solar masses, leaving behind a spinning black hole of 21 solar masses. The difference in total mass was converted to gravitational wave energy during the coalescence of the black holes.

“Because of their lighter masses compared to the first detection, they spent more time — about one second — in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe,” said LIGO spokesperson Gabriela Gonzalez, a professor of physics at Louisiana State University, in a statement released by the two groups.

According to the statement, the detectors — referred to as Advanced LIGO — will begin collecting data again in the fall of 2016, following upgrades that will permit probing as much as twice the volume of the universe.

The announcement of the second event comes soon after a successful proof-of-concept experiment with the LISA Pathfinder spacecraft, which showed that future orbiting detectors could in principle detect gravitational waves in other frequency bands.